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      <h1 class="post-title">Sql语句：分组最后一条</h1>

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        <span class="post-time"> 2017-01-10 </span>
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            <a href="/categories/mysql/"> mysql </a>
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      <p><a href="https://stackoverflow.com/questions/1313120/retrieving-the-last-record-in-each-group/1313293#1313293">https://stackoverflow.com/questions/1313120/retrieving-the-last-record-in-each-group/1313293#1313293</a></p>

<p>别笑，这个问题困惑了我很久，我曾经用过两个子查询的语句去做，导致性能挺差的，也试过用一张中间表去保存最后的
ID，结果因为莫名其妙的ID没有同步好，导致了一个BUG，退款了给别人，心塞啊。今天试着google了一下，原来这么容易就可以解决这个问题了，果然是所有的子查询都可以写成JOIN的形式。</p>

<p>场景 ： 比如一个日志表，有个订单号的字段，现在要取各订单号的最后一条日志</p>
<div class="highlight"><div class="chroma">
<table class="lntable"><tr><td class="lntd">
<pre class="chroma"><code class="language-sql" data-lang="sql"><span class="lnt">1
</span><span class="lnt">2
</span><span class="lnt">3
</span><span class="lnt">4
</span></code></pre></td>
<td class="lntd">
<pre class="chroma"><code class="language-sql" data-lang="sql"><span class="k">SELECT</span> <span class="n">m1</span><span class="p">.</span><span class="o">*</span>
<span class="k">FROM</span> <span class="n">messages</span> <span class="n">m1</span> <span class="k">LEFT</span> <span class="k">JOIN</span> <span class="n">messages</span> <span class="n">m2</span>
 <span class="k">ON</span> <span class="p">(</span><span class="n">m1</span><span class="p">.</span><span class="n">name</span> <span class="o">=</span> <span class="n">m2</span><span class="p">.</span><span class="n">name</span> <span class="k">AND</span> <span class="n">m1</span><span class="p">.</span><span class="n">id</span> <span class="o">&lt;</span> <span class="n">m2</span><span class="p">.</span><span class="n">id</span><span class="p">)</span>
<span class="k">WHERE</span> <span class="n">m2</span><span class="p">.</span><span class="n">id</span> <span class="k">IS</span> <span class="k">NULL</span><span class="p">;</span></code></pre></td></tr></table>
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<p>感谢解答了这个问题的大佬！</p>

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